The present invention relates generally to a fuel delivery system for a two-stroke engine and, more particularly, to a fuel delivery system that employs a combination of a single electric fuel pump in a dead-headed or returnless fuel supply network to deliver fuel to a two-stroke engine.
Fuel injection systems are used to supply fuel to many modern automobile engines because their ability to precisely meter fuel flow and accurately control the mixture of fuel and air delivered to an engine dramatically improves engine performance while reducing engine exhaust gas emissions. In one type of fuel injection system, a fuel pump transfers fuel under high pressure directly from a fuel tank to a fuel rail connected to the individual fuel injectors of the engine. Excess fuel not used by the fuel injectors during periods of low engine demand is returned to the fuel tank. Unfortunately, the returned fuel can vaporize or become aerated and foamy, which can lean out the air-fuel mixture delivered to the engine by the fuel pump.
As a result of recent passage of stringent emissions regulations and consumer demand for better performance, there is an increasing demand to employ fuel injection systems in two-stroke engines such as outboard marine engines. However, because the operating environment for outboard marine engines differs enormously from the operating environment for automobile engines, the design engineer faces considerable challenges not faced by the designer of automobile engines. For example, in order to prevent fuel from leaking from the fuel injection system and possibly igniting, U.S. Coast Guard regulations do not allow the use of a pressurized fuel line from a remote fuel tank to inboard engines. While outboards are typically exempt from the federal regulations, ABYC (American Board & Yacht Council) standards, which reflect the federal regulations, are generally applicable. U.S. Coast Guard regulations also prohibit the return of excess fuel from the fuel injectors to the fuel tank, as is typically done in automotive fuel injection systems. Hence, many fuel injection systems of the type commonly used in automobile engines are not usable in marine engines and some other two-stroke engines.
One proposed solution to the problem of injecting fuel in a two-stroke engine without requiring the use of a pressurized external fuel line or a fuel return system requires dual fuel pumps for delivering fuel to the engine. A fuel delivery system 80 incorporating this proposed solution is schematically illustrated in FIG. 1. The fuel delivery system 80 includes first and second fuel pumps 88 and 92 that are located in a fuel supply line 84 and that are collectively configured to pump fuel from a fuel tank 82 to fuel injectors of the engine. In use, fuel is transferred first, by suction through the fuel supply line 84 from fuel tank 82 to fuel pump 88 through a primer bulb 86. (The primer bulb 86 is used only to prime the system with fuel before the start-up.) From the first fuel pump 88, fuel is transferred through the fuel supply line 84 to a vapor separator 90, where entrained vapor in the fuel is removed via a vent 98. Finally, the second fuel pump 92 transfers fuel from the fuel supply line 84 to all of the fuel injectors at a second, higher pressure than the first pressure generated by the first fuel pump 88. A pressure regulator 96 regulates the fuel pressure to the fuel injectors from the second fuel pump 92. Excess fuel from the second fuel pump 92 returns through the pressure regulator 96 to the vapor separator 90 through a fuel return line 94. The returned fuel is then available for use by the second fuel pump 92.
The pumping of excess fuel needlessly wastes power. Consequently, the first fuel pump 88 and the second fuel pump 92 run more often than necessary and use more power than is needed to supply an adequate amount of fuel at an adequate pressure under most engine operating condition. Also, the return of fuel to the vapor separator 90 carries engine heat to the fuel delivery system 80 that can increase the temperature and create vapor in the fuel delivery system. The increased temperature may cause fuel to flash into a vapor, leading to an effect commonly referred to as vapor lock. Vapor lock can result in erratic engine operation, loss of power output, or even cause the engine to stall or overheat.
Another major disadvantage of the fuel delivery system 80 illustrated in FIG. 1 is that it requires two fuel pumps 88 and 92. In some outboards, the first pump is a lift pump and is crankcase pulse driven while the second pump is electric. In others, both are electric. This can be problematic because electrical power demands on boats are rising due to a proliferation of electrically powered devices. These devices include convenience lights, headlights, compact disc players, and fish-locaters, as well as other electric power consuming devices and instruments. Every effort is being made to minimize the electrical power consumption of all outboard marine engine components in order to permit the use of a relatively small battery and/or alternator. These efforts may be frustrated if the engine's electrical system must supply power to two separate electric pumps.
Although the above disclosed prior art has enjoyed acceptance, further improvements remain desirable. It would therefore be desirable to provide a dead-headed or returnless fuel delivery system with a single electric fuel pump, which is low in cost, and which enhances engine fuel economy.